1. Field of the Invention
The present invention relates to methods and apparatus for inserting pipes and/or tools into live well bore while maintaining pressure in the well bores and, also, to snubbing jack assemblies for use therein.
2. Description of the Related Art
All snubbing or live well operations require blowout preventors (BOPs) or other sealing devices to maintain the well pressure while operations take place. A standard blowout preventor configuration includes, from the bottom up, a double-gate BOP complete with blind rams that shut the flow of the well off in the event that there is no pipe or tools in the well bore; a set of pipe rams directly above the blind rams, within an double-gate BOP, that seals off the flow of the well in the event that there is pipe in it; a single gate stripping ram preventor, which is used when pipe is in the well and which is necessary to install tools into the well bore and/or land the tubing hanger into the well head; an equalizing spool complete with two ports and valving off each port for equalizing and bleeding off the pressure from with in the BOP configuration; and an annular BOP installed on the top of the equalizing spool. The annular blowout preventor is for sealing around the pipe while the pipe being inserted into the well, as well as sealing around non-standard shapes of tools, etc. Such tools may, for example, comprise bottom hole assemblies comprising combinations of different tools, which are site-specific, e.g. for setting-up wells and, performing remedial maintenance prior to actual production for assisting in the production of hydrocarbons from the wells. Plugs, packers, nipples, sleeves and blast joints are just some of the many tools that may be required in a typical bottom hole assembly. A single zone well may require nothing more than a profiled nipple with a plug in place to seal the flow of the fluid or gas from flowing up the tubing while it is being installed into the well while maintaining the well pressure at surface. When the tubing has been positioned to the desirable depth in the well and landed into the well head, the plug is recovered from the nipple, allowing flow up the tubing. The nipple may later be used to suspend pressure recorders (tools) in the well to monitor pressures of the zone while in a static and or flowing position. A dual-zoned well typically requires a nipple and plug to stop the flow during insertion of production tubing as well as a packer, a sliding sleeve and possibly a blast joint. The packer serves as a sealing device to segregate the two zones, so the top zone can be produced up the casing or annulus (the space between the tubing and casing) and the lower zone produced up the tubing simultaneously. The sliding sleeve functions as a device to be able to equalize differential pressures between the zones to assist in pulling or retrieving tools (plugs, pressure recorders etc.) from the profiled nipple as well as establishing communication between the tubing and casing to flow back or displace fluid, gas and or other materials from the top zone (above the packer) up the tubing. Because of the smaller inside diameter and ultimately the volume required to fill the tubing, a more desirable flow rate and pressure can typically be maintained while the flow back is taking place. Many zones have high static (shut in) pressures, but don't necessarily produce the volume required to fill larger areas such as the annulus fast enough to establish desirable a rate of flow. Many formations can be severely and irreversibly damaged when the pressure from the producing zone is flowed back at a rate faster then that of which the hydrocarbons can pass through the zone (rock, sand, clay etc.) drawing in water or oil from below the zone and restricting flow. The blast joint may serve as a tool to protect the tubing from the erosive effects the flow of fluid and/or particles of sand etc. in to the annulus.
The conventional method of lubricating or stripping-in, i.e insertion into a live well through the well head, is achieved by closing the stripping rams around the pipe, then bleeding off the pressure above. The annular BOP is then opened and the pipe and the tool assembly are lowered (i.e. the pipe is stripped through the stripping rams) into a space provided between the stripping rams and the annular BOP. When the tool assembly is in position, the annular BOP is closed and the pressure is equalized between the stripping rams and the annular BOP. The stripping rams are then opened. Normal operations then continue until the job has been completed.
In the event that the tools required to be lubricated into the well are longer than the space available in a conventional BOP configuration, an extended lubricating spool is installed to facilitate them.